The invention is related to a rolling element bearing, comprising an outer ring and an inner ring which enclose a bearing space containing rolling elements which are in rolling contact with the raceways of both rings.
Such rolling element bearings are widely known, and may take the form of for instance deep groove ball bearings, spherical or taper roller bearings, needle roller bearings etc. Generally, these types of bearings behave satisfactorily; however, under more demanding conditions such as in case of marginal lubrication, extreme temperatures and vibrations further improvements are necessary.
In this respect, proposals have been made to apply ceramic materials for the rings and/or rolling elements, such as silicon nitride, silicon carbide, aluminium oxide or cermets. Usually those materials are applied in combination with the normal steel parts.
Hybrid bearings (ceramic balls and steel rings) have been used successfully in some very specific applications, in particular, silicon nitride balls for high speed precision (spindle) bearings. The low density and high rigidity or stiffness of the silicon nitride plays a very important role in reducing the centrifugal force acting on the balls and the friction in contacts, thus giving excellent performance, in particular under marginal lubrication conditions.
The disadvantage of bearings having rings or rolling elements which are made with a combination of materials i.e. hybrid bearings, is that the different materials applied therein behave in a different way under loading and temperature. First of all, the specific weights thereof differ considerably, resulting in dynamic imbalances and non-uniform loading of the rolling elements. Moreover, due to the different thermal expansion coefficients, the internal bearing clearance cannot be maintained within the required boundaries. As a result, the useful service life of the bearings in question is impaired.